Immunostimulation as a therapeutic concept has long been known in medicine. In general, it is defined as the injection of substances which themselves have only weak if any antigenic effect, but are nevertheless able to induce the body's own defense mechanisms in a nonspecific or even specific manner. According to the data currently available, a great number of substances are able to stimulate immune defense, and especially various minerals, e.g., Al(OH).sub.3, MgSO.sub.4, beryllium, vegetable oils with or without added mycobacteria, as well as a number of constituents of plants can be mentioned among them. The substance class of the lectins should be mentioned in this connection in particular; their immunostimulating effect was investigated intensively. The lectins (phytohemagglutins) are plant proteins or glycoproteins. Polysaccharides are other plant constituents with immunostimulating effect which were isolated from lower and higher fungi, lichens and algae, and investigated. The entire complex subject of immunostimulation was described in detail e.g., by Chedid, L. et al. in Immunstimulation [Immunostimulation], Springer Verlag, Heidelberg, New York, 1980; Heidelberger, M.: Structure and Immunological Specificity of Polysacc[h]arides, Fortschritte d. Chem. org. Naturst., Vol. 42, pp. 288 (1982); and Drews, H.: Possibilities of Immunostimulation, Swiss Pharma, 2, 9 (49) (1980).
In most known cases it has been impossible to definitely clarify the exact mode of action of the immunostimulating substances. Among other things, these substances generally influence the proliferation of the immunocompetent cells, but they do not leave behind any memory reaction. This means that the primary targets of the action of the immunostimulating substances are the macrophages and granulocytes, as well as the T and B lymphocytes. The effect of the immunostimulants may be direct or indirect, e.g., via the complement system or the lymphocytes, via the production of interferon or lysosomal enzymes (e.g., lymphokines, colony-stimulating factor and others), as well as via an increase in macrophagocytosis and microphagocytosis. Cascade effects and simultaneous influences on a plurality of defense mechanisms are always to be expected because of the entanglement of nonspecific and specific defense mechanisms.
The preferred applications of immunostimulation in medicine are primarily the therapy of mixed infections and chronic, persistent, chemotherapy-resistant bacterial and viral infections, the prevention of opportunistic infections in patients at risk, the therapy of malignant diseases and, to a certain extent, also the treatment of autoimmune diseases. Immunostimulants can also be used in cytostatic therapy for partial compensation of the immunosuppression associated with such therapy.
A number of extraction methods have been described in the literature for isolating polysaccharides from starting materials of vegetable origin: Whistler, R. L. and J. L. Sannella: Methods in Carbohydrate Chemistry, editors: Whistler, R. L. and J. N. Bemiller, Vol. V, pp. 34-36, Academic Press, New York 1965; Tomoda, M., K. Shimada, Y. Saizo, and M. Sugi: Chem. Pharm. Bull., Vol. 28, No. 10, p. 2933 (1980).
Thus, depending on the type of polysaccharide, the plant material in question is extracted with cold or hot water, aqueous salt solutions, dilute acids or alkalies, or dimethyl sulfoxide. From the solutions thus obtained, the crude polysaccharide fraction is obtained, in general, by precipitation with alcohol, via complexing with heavy metal salts or quaternary ammonium salts. The crude polysaccharide fractions are then separated by ion exchange chromatography, gel filtration chromatography and bioaffinity chromatography.
The following disadvantages are inevitably associated with the isolation of polysaccharides from native starting plant materials according to the known methods. The lipophilic accompanying substances, e.g., chlorophyll, which are also obtained during the extraction, are difficult to separate, or they can be separated only after lengthy extraction with organic solvents. Depending on the nature of the native starting plant material, the crude polysaccharide fractions prepared are always obtained in both qualitatively and quantitatively different compositions by the various purifications of the same plant material. Another major disadvantage is the fact that it is absolutely necessary to use alkaline or acidic extractants, which are inevitable in the isolation of special polysaccharide types. The primary, secondary or tertiary structures of the polysaccharides are altered, and the immunostimulating effect is therefore influenced by the use of these extractants.
The object of the present invention is to present processes for isolating polysaccharides from higher plants which are free from the aforementioned disadvantages and permit simple and efficient preparation of polysaccharides from higher plants.
Another object of the present invention is to propose pharmaceutical formulations which contain the immunostimulating agents for use in human therapy.